A March 30, 2010, photo of the Guantanamo Bay detention facility in Cuba. (Brennan Linsley/Associated Press)

Gregory B. Craig was White House counsel in 2009. Cliff Sloan was special envoy for Guantanamo closure in 2013 and 2014.

As President Obama approaches the final year of his presidency, the urgency of closing the Guantanamo Bay detention facility looms large. Some maintain that the congressional ban on transfers from Guantanamo to the United States prevents closure without congressional approval. But that is wrong. Under Article II of the Constitution, the president has exclusive authority to determine the facilities in which military detainees are held. Obama has the authority to move forward. He should use it.

Despite difficulties and controversy, the president has made significant progress, slashing the number of detainees at the facility by more than half, to 112, the lowest level since it opened in 2002. The pace of transfers of cleared detainees to foreign countries has begun to tick up again and is expected to accelerate until all who can be transferred are gone. At least some current detainees, however, will need to continue to be incarcerated. Ten detainees, for example, face serious criminal charges in military commissions, including Khalid Sheik Mohammed and the other accused 9/11 co-conspirators.

Congress has enacted legislation banning the use of funds to transfer Guantanamo detainees to the United States for any purpose, including incarceration and prosecution. But that irrational prohibition need not inhibit the closure of the facility. The restriction is plainly unconstitutional.

The Constitution assigns Congress the important power to “declare war.” But Article II designates the president as “Commander in Chief” of the military. Recognizing that the president needs flexibility to select among tactical options in the conduct of war, the Framers explicitly rejected giving Congress the power to “make war,” rather than declare war. As Alexander Hamilton explained in the Federalist Papers, “Of all the cares or concerns of government, the direction of war most peculiarly demands those qualities which distinguish the exercise of power by a single hand.”

Thus the president, in his capacity as commander in chief, has the exclusive authority to make tactical military decisions. Congress can declare war but cannot direct the conduct of military campaigns. It can pass generally applicable military regulations but cannot direct the military’s response to contingent developments. It can authorize detentions and military tribunals and broadly regulate the treatment of prisoners of war, but it cannot direct specific facilities in which specific detainees must be held and tried. Yet that is precisely what Congress has attempted.

Congress’s purported ban on funding any movement of detainees from Guantanamo Bay to the United States restricts where “law-of-war” detainees can be held and prevents the president from discharging his constitutionally assigned function of making tactical military decisions. Accordingly, it violates the separation of powers.

The determination on where to hold detainees is a tactical judgment at the very core of the president’s role as commander in chief, equivalent to decisions on the disposition of troops and the use of equipment. The question here is not whether the president can unilaterally take the nation to war or hold detainees without congressional authorization. The question is whether Congress can tell the president where military detainees must be held. The answer is an emphatic no. One need not accept a particularly broad view of executive authority — let alone the Bush administration’s sweeping view that the president has “exclusive and virtually unfettered control over the disposition of enemy soldiers and agents captured in time of war” (an extravagant assertion with which we disagree) — to see that the restrictions Congress has imposed are unconstitutional.

Ironically, those who argue most vehemently for this restriction — and against closing Guantanamo — invoke the history of law-of-war detention. But this type of congressional intrusion is fundamentally at odds with that history. Decisions about the location of detention have long been understood to fall within the president’s exclusive purview. For example, during World War II, Congress passed general laws regulating the treatment of more than 7 million prisoners of war held by the United States — including some 400,000 housed in U.S. detention facilities — but it conspicuously did not specify in which facilities any particular prisoners could be held. Indeed, during the Persian Gulf War, amid concerns over resettling some former Iraqi soldiers in the United States, the only action Congress took was to pass a nonbinding “sense of the Senate” resolution.

Some have argued that the Guantanamo restriction is legitimate because it is a limitation on appropriated funds. But it makes no difference that Congress styled the ban as a funding restriction. Almost 70 years ago, in United States v. Lovett , the Supreme Court ruled that Congress may not use its appropriations power to achieve goals otherwise beyond its constitutional authority. Congress cannot, for example, condition military funding on a requirement that the president target a particular enemy combatant at a particular time and place. The principle is precisely the same with the location of detention and prosecution for detainees.

Obama has explained that Guantanamo “weakens our national security by draining resources, damaging our relationships with key allies and partners, and emboldening violent extremists.” Congress has tried to force the president to maintain a specific military detention facility for specific detainees that, in his judgment, is harmful to U.S. national security and far too costly. That is no way to conduct a war, and the Constitution does not permit it.

The president has attempted to work with Congress to eliminate the detainee transfer restrictions. From a practical standpoint, the constructive involvement of Congress would be helpful. But the president does not need Congress’s authorization to act. If Congress is unable or unwilling to work with him, Obama should use his exclusive authority as commander in chief to move the limited number of detainees who cannot be transferred to foreign countries to secure institutions in the United States, shutter this notorious facility, and end this blight on American values and national security.